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Images: If Rain Falls on the Ocean—Does It Make a Sound?

The Great Salinity Anomaly, a large, near-surface pool of fresher-than-usual water, was tracked as it traveled in the subpolar gyre currents from 1968 to 1982.

Salinity as a function of time at 10 meters, 200 meters, and 1,000 meters depth as recorded at Ocean Weather Station Bravo in the Labrador Sea. Deep convection is possible when the salinity difference between shallow and deep water is small. This normally occurs every winter. However, from 1968 to 1971, the presence of the fresh, shallow, Great Salinity Anomaly prevented deep convection. Unfortunately, Weather Station Bravo is no longer maintained. Scientists will need to use new technology like the PALACE float in order to reestablish such time series. Such data is essential for understanding the role of freshwater anomalies in the climate system.

Deep convection is a key component of the ocean’s role in Earth’s climate. Strong winter cooling of surface waters causes them to become denser than water below them, which allows them to sink and mix with deeper water. This process releases heat from the overturned water to the atmosphere and maintains northern Europe’s moderate winter climate. The Great Salinity Anomaly interrupted this process as its pool of fresher water prevented convection.

The average surface salinity distribution in the global ocean, as compiled from many individual ship measurements, mostly during this century. The figure also shows the approximate coverage obtainable with an array of about 1,000 Slocums or PALACES. These would resolve the large scale features of the salinity field and provide completely new information on its variability with time. The array would be an early warning system for the Great Salinity Anomalies of the future.